Major, Trace, and Rare Earth Elements Geochemistry of the Late Paleocene Shales from Gamba Formation, Sokoto Basin, Northwest Nigeria

Trace elements and major oxides geochemistry has gained global attention because of their potentials as provenance, tectonic settings, and paleoenvironmental reconstructions indicators in geological materials. Until now, there has been a lack of extensive focus on the detailed analysis of major, trace, and rare earth elements in the shales of the Sokoto basin, particularly within the Gamba Formation of the basin. Therefore, the present investigation delved into the geochemical importance of trace elements and major oxides constituents in the shales taken from the Gamba Formation, situated in the Sokoto basin. This was achieved through the utilization of inductively coupled plasma-mass spectrometry (ICP-MS), x-ray fluorescence spectroscopy (XRF), and statistical methodologies, all considered within the framework of provenance, tectonic environments, and conditions of deposition. Alkali metals and alkali-earth metal elements, Na, K, Ca, and Mg occurred in very high concentrations in the shale samples while U has the lowest values, indicating the detritus derived from various provenances (felsic and mafic) and reducing conditions of the environment. Among the rare earth elements detected in the shales, light rare earth elements showed enriched concentrations compared to heavy rare earth elements, indicating anoxic conditions. Among the major oxides identified, the shales exhibit elevated levels of SiO ₂ , with Fe ₂ O ₃ greater than Al ₂ O ₃ ; whereas the remaining oxides demonstrate relatively low concentrations. This suggests that shales are predominantly constituted of quartz minerals and were formed in marine settings. Moreover, the distribution patterns of the trace elements and major oxides showed striking similarities on the spider diagrams of UCC and PAAS. The ratios derived from both the trace elements and major oxides, along with the discrimination diagrams, indicated that the shales consist of mafic and felsic detritus. They were likely deposited under varying conditions, such as anoxic and oxic, in close proximity to the passive margin and continental island arc. These conclusions were further corroborated by the multivariate statistical analyses conducted on the elemental dataset. This study demonstrated the effectiveness of trace elements and major oxides geochemistry in assessing the origin, tectonic setting, and paleoenvironments of shales.